1. Field of the Invention
The present invention relates to a system for establishing a communication link between a caller and a mobile communication device. More particularly, the present invention relates to a system for establishing a communication link between a caller and a mobile communication device to permit automatic, transparent roaming by an operator of the mobile communication device.
2. Background Information
Mobile or cellular telephone systems were initially developed principally as local networks. In such a local network, an operator of a cellular telephone subscribes to a cellular carrier system which provides mobile telephone services in a particular geographic region.
In these local networks, the subscriber is provided with a cellular telephone number and/or mobile identification number (MIN). These numbers allow a caller to call the subscriber's mobile telephone when the mobile telephone is physically located within the geographic region serviced by the subscriber's cellular carrier. If the subscriber's mobile telephone is not located within that particular geographic region, at which time the subscriber is referred to as a "roaming subscriber" or "roamer", the carrier cannot provide direct access to the subscriber's mobile telephone. Hence, such local networks are limited in service performance.
Several conventional systems exist for providing mobile telephone services to a roaming subscriber. The simplest system requires a roaming subscriber to inform potential callers of his or her itinerary and give to the potential callers a different access number for each regional carrier system corresponding to each geographic region that the roamer intends to visit. In this system, any potential caller who does not have the appropriate access number cannot place a telephone call to the roaming subscriber. To contact the roaming subscriber in such a system, the caller dials the appropriate access number for the regional carrier system servicing the geographic region in which the caller believes the roamer is located. Typically, this call is a toll call for the caller.
A second conventional system which may allow for some form of roaming is described in U.S. Pat. No. 4,672,655 issued to Koch. In Koch, a caller dials a mobile subscriber's telephone number, which connects the caller to a call center. Then the caller enters the caller's telephone number, and in some cases a code number for the geographic region or the local area in which the mobile subscriber is to be located. The caller then hangs up. The call center formulates a data signal which includes the mobile subscriber's telephone number, the caller's telephone number, and possibly the geographic region code, and sends the signal to a ground radio station which uplinks the signals to a satellite. The satellite transmits the signal to transceivers corresponding to the geographic region in which the roamer is to be located. Each of the transceivers receives the signals and retransmits the received signals over the particular geographic area covered by that transceiver. If the mobile subscriber is located in an area covered by one of the transceivers, the mobile subscriber's telephone will receive the signals and store the telephone number of the caller. The subscriber's mobile telephone responds by transmitting the stored telephone number of the caller to a base radio station associated with a call center in the region in which the subscriber is located. That call center then places the subscriber's call to the caller via the public switched telephone network ("PSTN").
This second conventional system improves the ability of a caller to reach a subscriber's mobile telephone when the subscriber is roaming because it employs a satellite and a plurality of transceivers to cover a larger geographic area than the systems previously described. However, like the first system described above, this second system also requires that the caller be aware of the subscriber's location when calling the subscriber. Moreover, in addition to dialing the subscriber's telephone number, the caller must dial the caller's own telephone number and possibly a code identifying the region in which the subscriber is located. Hence, this system, like the first system, does not allow a caller to access a subscriber's mobile telephone by calling the subscriber's cellular telephone number or MIN, without having any knowledge of the subscriber's geographic whereabouts. In other words, these first two systems lack "transparency."
The Koch system is further disadvantageous because it does not provide for verifying a roaming subscriber's creditworthiness before connecting the subscriber to the caller. As cellular companies are discovering, this can result in hundreds of thousands of dollars of fraudulent cellular services, a cost which is ultimately borne by bona fide subscribers.
Another conventional system improves the transparency of the roaming process by forwarding calls from a subscriber's carrier system to a visited carrier system, an implementation sometimes referred to as "follow-me roaming." In such a system, the roaming subscriber must dial an access code or number, such as, for example, *31, when visiting a geographic region covered by a participating cellular carrier. The visited carrier system performs roamer validity checks or verifies a roamer's creditworthiness through a clearinghouse, which maintains subscriber databases to validate the creditworthiness of roaming subscribers. When the roamer is validated, the visited carrier system assigns a temporary local directory number (TLDN) to the subscriber. The visited carrier system then sends the TLDN to the subscriber's home carrier system. In response to calls for the subscriber placed to the home carrier system, the home carrier system invokes call forwarding using the TLDN. Thus, when a caller dials the subscriber's cellular telephone number or MIN, the call is forwarded by the home carrier system to the visited carrier system.
This "follow-me" service has advantages over the first two systems because, although the subscriber is roaming, a caller need only dial the subscriber's cellular telephone number or MIN. Toll charges from the home system to the visited system, along with airtime charges and any daily fixed roaming fees are charged to the roaming subscriber, not the caller. The "follow-me" service suffers some disadvantages, however, particularly from the perspective of the roaming subscriber who must re-register with each visited carrier and then re-register periodically for the same visited carrier. In some systems, for example, the roamer must re-register within 12 hours of the last mobile-originated call. If the roamer does not re-register, the TLDN is removed from the visited system and the "follow-me" feature is terminated. Conventional systems implementing follow-me services are also disadvantageous because not all geographic regions are covered by participating cellular carriers.
In a hybrid conventional system, carriers allow a roaming subscriber to select either follow-me roaming or a more conventional roaming. In such a hybrid system, the caller must call both the subscriber's home cellular carrier and the cellular carrier covering the geographic region in which the subscriber is roaming. In particular, if the subscriber selects the more conventional form of roaming, he or she dials a different access code in the visited system (for example *32). The visited carrier system then informs the subscriber's home carrier system of the subscriber's presence in the visited geographic region. In response to a call to the subscriber's cellular telephone number, the home carrier system connects the caller to a recorded announcement informing the caller of the roamer access number of the visited carrier system. After listening to the recorded message, the caller must hang up, and, if the caller desires to do so, place a second call by dialing the roamer access number, receiving a second dial tone, and then dialing the roaming subscriber's cellular telephone number or MIN to reach the roaming subscriber's mobile telephone. In this system, the caller pays any toll charges for the connection to the visited system.
This hybrid system has an advantage over the first system discussed above because the visited carrier system automatically notifies the home system of the roaming subscriber's presence in the geographic region covered by the visited carrier system when the roaming subscriber dials the access code. The subscriber thus does not need to inform potential callers of his or her itinerary. However, like the other conventional systems discussed, this hybrid system also lacks transparency, in that the caller must make a second telephone call, which is typically a toll call, to reach the subscriber. Further, as in the follow-me roaming system, the subscriber must notify the visited regional carrier of the subscriber's presence by dialing a code.
In each of the conventional systems described above, the roaming subscriber is required to take some specified action; thus, the systems are not "automatic" to the subscriber. The cellular industry, through activities of the Cellular Telecommunications Industry Association (CTIA) and the Telecommunications Industry Association (TIA), has developed a set of interim standards recommending methods for allowing for what they refer to as "automatic roaming." However, as will be discussed below, these standards do not provide for a truly automatic system for providing service to roaming subscribers, but merely provides for a system in which some portions of the system are automatic.
The interim standards, called IS-41, include automatic mechanisms for identifying the visited carrier system to the subscriber's home carrier system, establishing financial responsibility for the roaming subscriber, establishing a roamer service profile including a list of features, capabilities, and operating restrictions pertaining to the roaming subscriber in the visited system, and providing for call delivery to the roaming subscriber.
A system of automatic roaming using the IS-41 standards relies on two classes of database for determining a subscriber's location. The first class of database is home location registers (HLR's), which contain basic information, such as a MIN, pertaining to each subscriber in a particular carrier system the current location of the subscriber, an electronic serial number of the subscriber's mobile telephone, and permitted services and features. The second class of database is visitor location registers (VLR's), which contain information concerning roamers. Each HLR and each VLR may serve more than one cellular telephone system.
In the operation of a system of roaming using the IS-41 standards, a roamer is required to register in a visited carrier system. The registration may be initiated directly by the roamer, or a mobile telephone switching office (MTSO) of a visited carrier system may detect the roamer's presence from a call initiated by the roamer, a call completed to the roamer, or through a request for service. Once the registration has been initiated, the visited MTSO notifies its associated VLR that the roamer has registered. The VLR then sends a registration notification message to the HLR associated with the roamer's home carrier system. The message sent by the VLR is routed according to the roamer's MIN. If the roamer was previously registered with a different visited carrier system, the HLR sends a registration cancellation message to the VLR associated with the different carrier system.
After the new VLR sends the message to the HLR, the new VLR opens a record for the roamer, and the HLR records the identification of the visited system. The VLR may send a qualification request message to the HLR to verify the roamer's MIN and electronic serial number (ESN). The VLR may also send a service profile request to the HLR to determine the types of service the roamer is entitled to receive. The registration, qualification, and service profile requests may be sent as separate messages or may be transmitted all at once.
When a caller dials the roamer's MIN, the call is first routed to the mobile telephone switching office of the roamer's home carrier system, which interrogates the associated HLR with a location request to determine the current location of the roamer. The HLR responds by sending a routing request message to the VLR associated with the carrier system the roamer is visiting. The VLR passes the request to the mobile telephone switching office center of the visited carrier system to determine whether the roamer's mobile telephone is busy or idle. If the roamer's mobile telephone is idle, the visited MTSO assigns a TLDN to the roamer and returns the TLDN to the VLR. The VLR responds to the routing request by sending the TLDN to the HLR. The HLR then responds to the location request by sending the TLDN to the home MTSO. The home MTSO then forwards the call to the roamer using the TLDN.
This system, according to the IS-41 standards, suffers from the drawback that it is not truly automatic. As in the previously described systems, the roaming subscriber must register in a visited system by entering a code or by making a phone call from the visited region.